The present invention relates to multiplexed data signals and, ore particularly, to a circuit for monitoring a multiplexed data stream to generate signals representative of a variety of characteristics of the multiplexed data stream and especially representative of signal level changes within the multiplexed data stream.
It is oftentimes necessary or desirable to transmit several signals occupying the same time range over a single channel. Various well-known modulation techniques referred to generically as multiplexing allow the signals to share the same channel and yet be recovered separately. Multiplexing, for example, permits the number of channels in a transmission system or conductors in a cable to be reduced for size and economy considerations.
As the number of signal sources in a multiplex data system increases, it may be desirable to arrange the sources into banks of sources with each bank comprising a fractional number of the total sources. For an orderly arrangement, it is convenient to organize the banks as columns of a matrix with the individual sources of the banks being in different rows of the matrix. Each bank or column is assigned to a specific time slot or portion of the multiplexed signal with the signal from one source in each of the columns being sampled during a given time interval which is referred to as a frame of the multiplexed signal.
For all of the sources of a large, matrix organized multiplex system to be sampled, a number of frames equal to the number of rows of the matrix must be transmitted with a different source from each column being sampled during each frame. In such a matrix arrangement, a multiplex bus is provided to connect the signal generating sources and a remote user of the signals generated by the sources. The multiplex bus may have a control line corresponding to each row of the matrix, in which event, the interconnecting channel comprises: the multiplexed data from all the signal sources; a frame synchronizing signal; a data clock defining when data is valid in each time slot; and, one line for each row of signal sources such that the active row for each time slot can be indicated.
Such a multiplexing arrangment functions quite well unless the number of signal sources is so great that the time between samples for a given signal source becomes excessive such that the sample frequency is less than the transition frequency of the signal source.